CO2 emissions turn oceans to acid

Soaring carbon dioxide levels have begun to make the oceans more acidic, Britain's most senior scientists warn. Exhausts from fossil fuels have already increased the acidity to a level that cannot be reversed in a human lifetime. Only swift and drastic cuts in emissions could begin to stabilise the oceans by 2100.

A Royal Society report published yesterday warns that many of the biological and chemical processes in the ocean have yet to be understood. But after a preliminary survey, scientists fear that:

· cold water corals, shellfish, starfish and sea urchins could have difficulty making their calcium carbonate shells and skeletons

· larger fish might gradually find it more difficult to breathe

· squid and some deep sea fish would swim more slowly because less oxygen would be available

· plankton and other small creatures at the base of the food chain could be affected

· levels of toxic metals dissolved in coastal waters could increase

· tropical and subtropical coral reefs could become rare by 2050.

John Raven, of the Univer sity of Dundee, who headed the Royal Society's working group, said: "Our world leaders meeting at next week's G8 summit must commit to taking decisive and significant action to cut carbon dioxide emissions.

"Failure to do so may mean that there is no place in the oceans of the future for many of the species and ecosystems that we know today."

Oceans soak up much of the carbon dioxide produced by living organisms, either as dissolved gas, or in the skeletons of tiny marine creatures that fall to the bottom to become chalk or limestone. But in water, carbon dioxide becomes a weak carbonic acid, and the increase in the greenhouse gas since the industrial revolution has already altered the average pH - the laboratory measure of acidity - significantly and will go on doing so for at least 100 years.

The scientists warn that there is no hope of a technological fix. To neutralise the rising acidity, engineers would have to quarry a lump of chalk or limestone 100 metres deep and 40 miles square in area, every year, and sprinkle it across the oceans: in effect they would have to return the white cliffs of Dover to the seas.